Two pair is not just two pair. If you defended your blinds with KJ, and flop comes KJ4, then it would typically be a mistake to get away even with deep stacks, and if your opponent turns over 44 or the very unlikely KK or JJ, its just a cooler. However if you defended with JT, and flop comes AJT, then you are behind to quite a few hands in the preflop raisers range, and if you raise the flop, its probably an overplay. So instead you should just check-call, and if he continue to fire big bets on the turn and river, it can certainly be an option to fold depending on the runout and the opponent.
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